Entomopoxviruses (EPV's) are the most distant relatives of vertebrate orthopoxviruses (OPV's) such as vaccinia (VV) and variola (smallpox). Vertebrate poxviruses, are particularly masterful in deflecting the immune and other defense responses of the infected host. We have completed the genomic sequence of the EPV from Amsacta moorei (AmEPV), one of the few EPV's which can be easily grown in cell culture and readily manipulated. AmEPV, causes a lethal, disseminated infection of insects but is devoid of the immune modifier genes known to act as virulence factors of vertebrate poxviruses. We plan to focus on the major aspects of AmEPV infection of Lymantria dispar (LD) larvae as a model for the pathogenesis of poxviruses in lower eukaryotes. We have three Specific Aims. The first Specific Aim is to quantify and completely characterize the pathobiology of larvae infected with AmEPV by either direct injection or by feeding (per os). These studies will include a full time course of infection, evaluation of spread, yields and cellular involvement. In our second Specific Aim, we will determine why AmEPV, unlike any other known poxvirus encodes a third or "extra" subunit of the viral encoded poly (A) polymerase, an enzyme essential for viral mRNA synthesis. This unusual feature of the virus promises insight into some of the basic biology of gene expression governing all poxviruses. In our third Specific Aim, we will examine the role of specific genes on the pathobiology of AmEPV infections. We will initially concentrate on a "Kunitz-type" protease inhibitor and a 1365 amino acid ABC transporter gene neither of which have been reported in any other virus. We will begin by generating "knockouts" using a procedure which by design will also tell us whether the gene is essential for growth. Virus deleted for the selected gene will be evaluated for effects on pathogenesis. We also plan to extend these studies and examine virus encoded superoxide dismutase (SOD) and inhibitor of apoptosis protein (IAP) as examples of other genes likely to play significant roles in the infectious process. Each gene will be evaluated for biochemical function. Collectively, the proposed experiments will elucidate added diversity by which viruses counter the defenses of host organisms.